This invention relates to the detection of a blood clot and more particularly to the in vitro detection of a fibrin clot in a whole blood or blood plasma sample.
In vitro blood coagulation tests are performed clinically for purposes of analyzing the status of a patient's hemostatic or blood coagulation processes as such processes may relate to therapies or natural condition. The practice of in vitro blood coagulation analysis may be broken down into two categories. The first of these relates to indirect methods, usually involving some form of assay in which the analyte is an enzyme, clotting factor or medication and the effect upon ultimate in vivo thrombus formation is implied from the in vitro determination analyte concentration. The second category relies on clot time, that is an in vitro analysis of the time required for a blood sample or blood sample/reagent mixture to be transformed from its liquid state to one in which polymerized solid material is detected. Inferred from data resulting from clot timing analysis is the tendency for the in vivo formation of polymerized solid material.
Clot timing methods are further broken down into two approaches, photo-optical (turbidometric) and mechanical. Turbidometric clot sensors are generally limited to analyses of essentially transparent blood plasma samples. Mechanical methods, on the other hand, typically identify solidified material in a whole blood or plasma sample by making direct physical contact with the solidified material. In one such mechanical detection system, forces are directed from one mechanical element through the fibrin mass, to another mechanical element, a magnet. The resulting change in position of the latter is interpreted electronically by a magnetic field sensitive component to be indicative of the presence of a clot (see U.S. Pat. No. 3,695,842-METHOD AND SYSTEM FOR ANALYZING A LIQUID by M. Mintz issued on Oct. 3, 1972.) In another mechanical clot detection system, a needle is passed through a drop of blood and is examined for the presence of fibrin strands as it is withdrawn from the liquid surface (see Osgood, Edwin D. A TEXTBOOK OF LABORATORY DIAGNOSIS, 3rd. Ed., The Blakiston Company,. Philadelphia, 1940, p. 503). An automated embodiment of the "drop and needle method" is described in U.S. Pat. Nos. 3,267,362; 3,267,363; 3,267,364 and 3,268,804 wherein a fibrin strand is withdrawn from a liquid blood sample and thereafter comprises an electrically conductive path for signaling the occurrence of the clot-forming process. In an additional mechanical clot-detection scheme, a blood sample is drawn into a glass capillary tube from which small lengths are broken from one end at prescribed time intervals. The visual observation of a fibrous strand joining the broken and primary pieces of tubing is interpreted as an end point for clot detection (see Frankel and Reitman, Ed. GRADWOHL'S CLINICAL LABORATORY METHODS AND DIAGNOSIS 6 Ed. The C. V. Mosby Company, Saint Louis, 1963, p. 1199).
Some perceived disadvantage of the described prior art systems include moderate sensitivity, large blood sample volume requirements, inconvenience with regard to repetitive testing systems and occasionally unreliable test results.
Accordingly, it is the object of the present invention to provide an improved method and apparatus for reliably detecting the presence of a fibrous blood clot.
It is an additional object of the present invention to minimize blood sample volume requirements such that a multiplicity of coagulation timing tests on a single patient that utilize the invention may be performed without undue hazard to the patient.
It is an additional object of the present invention to provide a means whereby blood samples may be automatically collected from a vessel, transferred to a test zone and clot detection implemented.
It is still a further object of the present invention to provide a system whereby blood samples may be drawn into a collecting syringe and the test to identify fibrin clot formation performed within the body of the syringe itself.